Roadway markers are utilized in a variety of traffic control situations. Many roadway markers are affixed to a roadway to permanently delineate lanes of traffic on the roadway. Other roadway markers are used to temporarily delineate construction or work areas. Both permanent and temporary roadway markers are attached to a roadway with a suitable adhesive.
Permanent roadway markers have a low profile and remain in place to permanently define traffic lanes, identify obstacles, and perform other well-known functions, such as providing daytime visibility, and night time reflectivity, especially on wet nights when flush pavement markers disappear under a film of water. While having a low profile, many permanent roadway markers are raised to create a rumble sound in an automobile when the tires of the automobile impact a row of markers. The most commonly used permanent marker is formed of ceramic and has a partially hemispherical, button-like shape. In recent years, alternative roadway markers having inclined surfaces covered with a retroreflective medium in the form of a surface tape or embedded prisms have been developed for use as permanent roadway markers.
Many firms currently market roadway markers similar to that illustrated in U.S. Pat. No. 3,332,327. One example of such a product is the Model 88 sold by Stimsonite Corporation. Similar products are sold by Ray-o-lite Div. of Pac-Tech, Pavement Markers, Inc., and Apex International. The shells of these markers are variously transparent or opaque and have the form of a truncated pyramid. One or two lenses are either insert molded or molded integrally into the sides of these markers. The lenses are made retroreflective by including large cube-corner patterns on the inside of the sloped faces. After coating these inner faces with a light-reflecting material, e.g., aluminum, the plastic shell is filled with a relatively rigid material such as epoxy resin and the bottom surface covered with sand or glass beads to enhance the adhesion of the marker to the roadway.
Other roadway markers, essentially the same as those aforementioned in many ways, but differing in either shape or lens construction, are also currently available. The Stimsonite Model 948 is more elongated and lower in profile, but narrower in width. The Ray-o-lite Model 2001 has a similar shape. The markers of the type discussed in U.S. Pat. No. 4,726,706, such as the Stimsonite 953, differ in lens construction. Their lenses are "air-gap" reflectors rather than metallized like previous markers. The marker described in U.S. Pat. No. 4,875,798 is roughly the same shape as the Stimsonite Model 948, but is not filled and utilizes a reflective sheeting rather than an integrally molded reflective lens.
As is pointed out in many of the foregoing patents, the outer face of prior markers are sloped from the roadway at an angle large enough for good reflectivity and small enough to allow a wiping action by vehicle tires, i.e., from 15.degree. to 45.degree. and preferably 30.degree. to the surface of the road. The reflective materials used are either methyl methacrylate or polycarbonate. Both of these materials exhibit good optical qualities but are either extremely brittle, abrade very easily, or both. To overcome the problems associated with these characteristics, the Stimsonite Model 948 bonds a thin veneer of untempered glass to the outside face of the reflector. See U.S. Pat. No. 4,340,319. Ray-o-lite reportedly uses a chemical treatment that purports to do the same. Both of these solutions to the brittleness and abrasive problem are, from a manufacturing point of view, expensive. Further, they are unsatisfactory. In the case of the Stimsonite Model 948, the glass is very thin and still abrades quite readily. The Ray-o-lite product, while abrasion resistant, turns dark when installed on the road, thus rendering the marker substantially ineffective.
The marker described in U.S. Pat. No. 4,875,798 utilizes a very thin (2 mm) reflective sheeting for its reflective lens. The lens as disclosed lies at an angle from 15.degree. to 45.degree. to the roadway. This exposes the face of the lens to a tremendous amount of abuse by vehicle tires. After a short amount of time the reflectors of these markers become abraded, and begin to peel off of the marker body, thus reducing their effectiveness.
The sheeting described in U.S. Pat. No. 4,588,258 (Hoopman) incorporated into the marker described in U.S. Pat. No. 4,875,798 (May) is made of a rigid thermoplastic such as polycarbonate, as noted in the May patent. While these patents do not disclose whether the sheeting is or is not metallized, markers incorporating this technology have been produced both with and without metallization. Both types are initially quite bright, as predicted in the patent. However, over a long period of time, the reflectors fail due to the forces described above.
As noted above, abrasion is one of the major problems faced by roadway markers, particularly permanent roadway markers. Abrasion becomes particularly acute when pavement markers are used in areas where abrasive materials, such as sand and salt, are distributed over the roadway surface during the winter months. The sand and salt are continuously brought into contact with the reflectors of the pavement markers of the type described above by the wiping action of the tires. The combination of the abrasive materials and the wiping action of the tires tends to scratch the surface of the reflective lenses of such markers, rapidly diminishing their optical effectiveness and reflective quality.
High speed photography has revealed that the area of a typical marker that receives the most abuse is the "shoulder" of the marker, where the planes of the reflector face and the top of the marker join. At the initial impact, a tire rests on the pavement just in front of the marker and on the shoulder of the marker. Contrary to what is stated in a number of patents, the tires never "wipe" the face of the markers clean. Whatever wiping occurs is due to the effect of high speed jets of air and, when the road is wet, water that is carried in the tread of the tire. It is estimated that the speed of this air and water stream is in the vicinity of 250 feet/second. It is the speed of the water, not the action of tires that cleans pavement markers.
The action of the tire on the face of the marker is entirely deleterious. The tire scurfs, abrades, and coats the marker shoulder with black marks. Obviously it would be desirable to provide a raised pavement marker that obtains the positive effect of the air/water stream without the negative effects of an actual tire impact on the reflective lens of the marker. As discussed more fully below, the present invention achieves this result by providing a raised pavement marker with a curved front face. The radius of curvature is only slightly less than the radius of the tire as it ramps over the marker. As a result, while the tire does not wipe the face of the marker, the air/water stream benefit is retained.
Temporary roadway markers serve to notify motorists that a construction area is near and that caution is needed. They often direct roadway traffic to pass along the portions of the roadway unaffected by construction, while protecting workers within a construction area from roadway traffic. After construction is completed, temporary roadway markers are loosened and removed. To be effective, temporary roadway markers must alert traffic to the presence of a construction area. Typically, temporary roadway markers warn oncoming motorists by the use of visual cues, such as reflective surfaces. Some temporary roadway markers also use physical cues, such as causing a vehicle to create a rumbling noise on contact with a marker.
Temporary roadway markers are designed and manufactured so as to only last a short period of time-the life of a typical construction project, for example, six months. As compared to permanent roadway markers, temporary roadway markers in general are much more simplistic in construction, less expensive to manufacture, and lower in performance standards both initially and over time. The Stimsonite Model 66 and the roadway marker described in U.S. Pat. No. 4,428,320 (Oplt et al.) are both examples of temporary roadway markers. The Stimsonite Model 66 includes an air-gap reflector angled at 45.degree. to provide night visibility. In actual use the Stimsonite Model 66 marker provides very little initial reflectivity (66% lower than a permanent marker), which quickly fades with time. The molded lenses crack when the honeycombed body of the marker crushes under vehicle impacts. Water and dirt then get into the air-gap and eliminate reflectivity in the entire lens. The sheeting of the Oplt et al. marker is a much more efficient reflector. Being an embossed metallized polycarbonate microprism and mounted at an angle of 72.degree., it provides as much reflectivity as the "permanent" markers do, and for a much lower manufacturing cost. However, the reflective tape must be mounted within 20.degree. of the vertical in order to maintain its effectiveness, due to the structure of the embossed cube-corner microprisms. The honeycombed interior of the Oplt et al. marker makes the marker lightweight, which is desirable. Although the roadway marker is lightweight, one disadvantage of an Oplt et al. type roadway marker is its high manufacturing cost. Due to its construction, an Oplt et al. type roadway marker must be injection molded. Injection molding is expensive when compared to other manufacturing processes.
Another disadvantage of Oplt et al. and Stimsonite Model 66 temporary roadway markers is the fact that they are usually molded from a low cost resin such as high impact polystyrene in such a fashion as to reduce the weight of the final part. What results is a marker with a honeycombed base pattern that is essentially hollow. Because such markers are extremely sensitive to the impact of vehicle tires they do not last long on the road, often less than 30 days. As best understood at present, the typical vertical forces exerted on a raised marker by a small passenger vehicle tire are 200 ft. lbs. Larger vehicles can increase this force to as high as 1,000 ft. lbs. In testing, neither the Stimsonite Model 66 nor the Oplt et. al. type marker was found able to withstand even 60 ft. lbs. of vertical force. Another problem that arises with the use of hollow markers is that of adhesion to the roadway. Quite often installation contractors will eschew the use of more permanent adhesives and bond the markers with an elastomeric adhesive, such as a synthetic butyl rubber pad. The effect of the hollow marker on butyl is to cut through it like a cookie cutter, placing the plastic marker in direct contact with the pavement, resulting in immediate breakage, loss of adhesion, or both.
In order to overcome the costs disadvantage associated with injection molding, roadway markers having a constant cross-sectional shape along their longitudinal axis have been developed. The constant cross-sectional shape allows such roadway markers to be made by an inexpensive extrusion manufacturing process. Such roadway markers are described in parent U.S. patent applications Ser. No. 07/735,321 and Ser. No. 07/694,873 more fully referenced above, the subject matter of which applications is incorporated herein by reference.
In addition to their constant cross-sectional shape, roadway markers of the type described in the foregoing patent applications include a base area suitable for adhesive attachment to a roadway surface, as well as a raised rumble portion. The base area of the marker is relatively large and includes a plurality of adjacent, parallel grooves of arcuate cross section. The arcuate grooves increase the adhesive surface of the marker. The longitudinal lower edges of the base curve downwardly to assist in gripping the roadway surface. The top of the raised rumble portion is scalloped to reduce the weight of the roadway marker. The longitudinal lateral sides of the raised rumble portion of the roadway marker may include a recess for receiving a strip of reflective tape. The two orthogonal sides are sheared straight, or inclined, depending upon the intended use of the marker.
While extruded roadway markers of the type described above have a number of advantages over previously developed roadway markers of the injection molded type, previously developed extruded roadway markers, like injection molded roadway markers are subject to improvement, particularly in the area of viewability over extended periods. The present invention is directed toward providing roadway markers, particularly extruded roadway markers having improved viewability over extended periods of time.